Nowadays, liquid crystal display devices are broadly used in electronics devices such as monitors, projectors, mobile phones, and personal digital assistants (PDA). Such liquid crystal display devices can be classified into three types: a reflective type, a transmissive type, and a transflective type.
A transflective type liquid crystal display device performs transmissive display by utilizing light from a backlight under a condition of relatively dark illumination, for example, indoors, whereas performing reflective display with use of illumination light under a condition of relatively bright illumination, for example, outdoors. This feature makes it possible to accomplish a high-contrast-ratio display regardless of surrounding brightness. That is, the transflective type liquid crystal display device can perform display under any illumination condition (in any light environment), both indoors and outdoors. Therefore, the transflective type liquid crystal display devices have been broadly provided in mobile devices such as mobile phones, PDAs, and digital cameras.
A liquid crystal panel of such a transflective type liquid crystal display device includes two types of display regions including a reflective region (reflective display region) used for a reflection mode and a transmissive region (transmissive display region) used for a transmission mode.
In a standard transflective type liquid crystal display device, a λ/4 wavelength plate (hereinafter, simply referred to as λ/4 plate) needs to be provided on a front side (a side from which external light enters) of a liquid crystal layer so that a reflective display region can perform precise black and white display (See [Background Art] of Patent Literature 1, for example). Moreover, in a transmissive display region, another λ/4 plate needs to be provided on a back side of the liquid crystal layer so that an influence of the λ/4 plate provided on the front side of the liquid crystal layer is cancelled.
Furthermore, if the λ/4 plate were a perfectly ideal one, the plate would cause no problem. In general, however, characteristics of the λ/4 plate vary in accordance with wavelengths, and wavelength dispersion occurs. This results in a change in a tinge (chromaticity) in the reflective display region. The change in a tinge indicates, for example, a case where black is displayed as black tinged with blue and a case where white is displayed as white tinged with yellow.
Patent Literature 1 discloses a technique for correcting such a change in a tinge. In a configuration of the technique, two polarization plates are provided so as to sandwich a liquid crystal layer and phase difference compensation means (λ/2 plate) is provided between each of the polarization plates and the liquid crystal layer. This corrects such a tinge.
Moreover, Patent Literature 2 discloses a technique for compensating, by providing an optical thin film on a reflective electrode, a tinge of yellow in a liquid crystal layer in a reflective type or transflective type liquid crystal display device. Furthermore, the following configuration is disclosed in Patent Literature 3. In the configuration, a liquid crystal display device having a reflection function includes a first electrode formed from a thin film electrode that is formed from a transparent material directly covering the reflective layer. This is for the purpose of allowing the first electrode and a second electrode sandwiching the liquid crystal layer to have the same characteristics. In this configuration, a tint of a reflective display and reduction in reflectance in reflective display can be prevented by changing a thickness of the thin film electrode.
As described above, various studies are made for a technique for preventing a tint of a reflective display, in a liquid crystal display device having a reflection function.
Citation List
Patent Literature 1
Japanese Patent Application Publication, Tokukai, No. 2003-149636 A (Publication Date: May 21, 2003)
Patent Literature 2
Japanese Patent Application Publication, Tokukai, No. 2001-66585 A (Publication Date: Mar. 16, 2001)
Patent Literature 3
Japanese Patent Application Publication, Tokukai, No. 2003-255378 A (Publication Date: Sep. 10, 2003)